BOTANY 



Fio. 92. Three stages in the division of a 

 living cell of Epipactis paliistrls. (After 

 TREUB, x 365.) 



and their number is increased by the interposition of others (Fig. 

 86, 10). In consequence of this a barrel-shaped figure is formed, 

 which eithe/ separates entirely from the developing daughter nuclei, 

 or remains in connection with them by means of a peripheral sheath, 

 the CONNECTING UTRICLE. The first is the case in cells rich in cyto- 

 plasm, the latter when the cells are more abundantly supplied with 



cell sap. At the same time the con- 

 necting fibres become thickened (Fig. 

 86, 10) at the equatorial plane, and 

 the short rod-shaped thickenings form 

 what is known as the CELL PLATE. 

 In the case of cells rich in proto- 

 plasm or small in diameter, the con- 

 necting fibres become more and more 

 extended, and touch the cell wall at 

 all points of the equatorial plane (Fig. 

 86, 11). The elements of the cell 

 plate unite and form a cytoplasmic 

 limiting layer, which then splits into 

 two. In the plane of separation the new partition wall is formed 

 of cell-wall substance, and thus SIMULTANEOUSLY divides the mother 

 cell into two daughter cells (Fig. 86, 12). If, however, the mother cell 

 has a large sap cavity, the connecting utricle cannot at once become so 

 extended, and the partition wall is then formed SUCCESSIVELY (Fig. 

 92). In that case, the partition wall first commences to form at the 

 point where the utricle is in contact with the side walls of the mother 

 cell (Fig. 92 A}. The protoplasm then detaches itself from the part 

 of the new wall in contact with the wall of the mother cell, and 

 moves gradually across until the septum is completed (Fig. 92 B 

 and 0) ; the new wall is thus built up by successive additions from 

 the protoplasm. * 



The connecting fibres of the spindle consist of kinoplasm. The origin of the 

 cell plate from swellings of these fibres indicates its kinoplasmatic nature also. By 

 the splitting of the cell plate the limiting layers of the two sister cells are com- 

 pleted across the place of separation. The separation of the complex of connecting 

 fibres into two halves effects an equal division of the kinoplasm between the two 

 new cells. 



In the Thallophytes, even in the case of uninuclear cells, the 

 partition wall is not formed within connecting fibres, but arises 

 either simultaneously from a previously formed cytoplasmic plate, or 

 successively, by gradual projection inwards from the wall of the 

 mother cell. It was a division process of this kind (Figs. 93, 94), 

 first investigated in fresh-water Algae, that gave rise to the conception 

 of cell division, which for a long time prevailed in both animal and 

 vegetable histology. In this form of cell division the new wall com- 



